virtio_console: Add support for remoteproc serial

Add a simple serial connection driver called
VIRTIO_ID_RPROC_SERIAL (11) for communicating with a
remote processor in an asymmetric multi-processing
configuration.

This implementation reuses the existing virtio_console
implementation, and adds support for DMA allocation
of data buffers and disables use of tty console and
the virtio control queue.

Signed-off-by: Sjur Brændeland <sjur.brandeland@stericsson.com>
Acked-by: Amit Shah <amit.shah@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

2 files changed, 170 insertions, 23 deletions

diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c
index 548224686963..55a89a4ae42f 100644
--- a/drivers/char/virtio_console.c
+++ b/drivers/char/virtio_console.c
@@ -37,8 +37,12 @@
 #include <linux/wait.h>
 #include <linux/workqueue.h>
 #include <linux/module.h>
+#include <linux/dma-mapping.h>
+#include <linux/kconfig.h>
 #include "../tty/hvc/hvc_console.h"
 
+#define is_rproc_enabled IS_ENABLED(CONFIG_REMOTEPROC)
+
 /*
  * This is a global struct for storing common data for all the devices
  * this driver handles.
@@ -112,6 +116,15 @@ struct port_buffer {
         /* offset in the buf from which to consume data */
         size_t offset;
 
+        /* DMA address of buffer */
+        dma_addr_t dma;
+
+        /* Device we got DMA memory from */
+        struct device *dev;
+
+        /* List of pending dma buffers to free */
+        struct list_head list;
+
         /* If sgpages == 0 then buf is used */
         unsigned int sgpages;
 
@@ -331,6 +344,11 @@ static bool is_console_port(struct port *port)
         return false;
 }
 
+static bool is_rproc_serial(const struct virtio_device *vdev)
+{
+        return is_rproc_enabled && vdev->id.device == VIRTIO_ID_RPROC_SERIAL;
+}
+
 static inline bool use_multiport(struct ports_device *portdev)
 {
         /*
@@ -342,11 +360,13 @@ static inline bool use_multiport(struct ports_device *portdev)
         return portdev->vdev->features[0] & (1 << VIRTIO_CONSOLE_F_MULTIPORT);
 }
 
-static void free_buf(struct port_buffer *buf)
+static DEFINE_SPINLOCK(dma_bufs_lock);
+static LIST_HEAD(pending_free_dma_bufs);
+
+static void free_buf(struct port_buffer *buf, bool can_sleep)
 {
         unsigned int i;
 
-        kfree(buf->buf);
         for (i = 0; i < buf->sgpages; i++) {
                 struct page *page = sg_page(&buf->sg[i]);
                 if (!page)
@@ -354,14 +374,57 @@ static void free_buf(struct port_buffer *buf)
                 put_page(page);
         }
 
+        if (!buf->dev) {
+                kfree(buf->buf);
+        } else if (is_rproc_enabled) {
+                unsigned long flags;
+
+                /* dma_free_coherent requires interrupts to be enabled. */
+                if (!can_sleep) {
+                        /* queue up dma-buffers to be freed later */
+                        spin_lock_irqsave(&dma_bufs_lock, flags);
+                        list_add_tail(&buf->list, &pending_free_dma_bufs);
+                        spin_unlock_irqrestore(&dma_bufs_lock, flags);
+                        return;
+                }
+                dma_free_coherent(buf->dev, buf->size, buf->buf, buf->dma);
+
+                /* Release device refcnt and allow it to be freed */
+                put_device(buf->dev);
+        }
+
         kfree(buf);
 }
 
+static void reclaim_dma_bufs(void)
+{
+        unsigned long flags;
+        struct port_buffer *buf, *tmp;
+        LIST_HEAD(tmp_list);
+
+        if (list_empty(&pending_free_dma_bufs))
+                return;
+
+        /* Create a copy of the pending_free_dma_bufs while holding the lock */
+        spin_lock_irqsave(&dma_bufs_lock, flags);
+        list_cut_position(&tmp_list, &pending_free_dma_bufs,
+                          pending_free_dma_bufs.prev);
+        spin_unlock_irqrestore(&dma_bufs_lock, flags);
+
+        /* Release the dma buffers, without irqs enabled */
+        list_for_each_entry_safe(buf, tmp, &tmp_list, list) {
+                list_del(&buf->list);
+                free_buf(buf, true);
+        }
+}
+
 static struct port_buffer *alloc_buf(struct virtqueue *vq, size_t buf_size,
                                      int pages)
 {
         struct port_buffer *buf;
 
+        reclaim_dma_bufs();
+
         /*
          * Allocate buffer and the sg list. The sg list array is allocated
          * directly after the port_buffer struct.
@@ -373,11 +436,34 @@ static struct port_buffer *alloc_buf(struct virtqueue *vq, size_t buf_size,
 
         buf->sgpages = pages;
         if (pages > 0) {
+                buf->dev = NULL;
                 buf->buf = NULL;
                 return buf;
         }
 
-        buf->buf = kmalloc(buf_size, GFP_KERNEL);
+        if (is_rproc_serial(vq->vdev)) {
+                /*
+                 * Allocate DMA memory from ancestor. When a virtio
+                 * device is created by remoteproc, the DMA memory is
+                 * associated with the grandparent device:
+                 * vdev => rproc => platform-dev.
+                 * The code here would have been less quirky if
+                 * DMA_MEMORY_INCLUDES_CHILDREN had been supported
+                 * in dma-coherent.c
+                 */
+                if (!vq->vdev->dev.parent || !vq->vdev->dev.parent->parent)
+                        goto free_buf;
+                buf->dev = vq->vdev->dev.parent->parent;
+
+                /* Increase device refcnt to avoid freeing it */
+                get_device(buf->dev);
+                buf->buf = dma_alloc_coherent(buf->dev, buf_size, &buf->dma,
+                                              GFP_KERNEL);
+        } else {
+                buf->dev = NULL;
+                buf->buf = kmalloc(buf_size, GFP_KERNEL);
+        }
+
         if (!buf->buf)
                 goto free_buf;
         buf->len = 0;
@@ -446,7 +532,7 @@ static void discard_port_data(struct port *port)
                 port->stats.bytes_discarded += buf->len - buf->offset;
                 if (add_inbuf(port->in_vq, buf) < 0) {
                         err++;
-                        free_buf(buf);
+                        free_buf(buf, false);
                 }
                 port->inbuf = NULL;
                 buf = get_inbuf(port);
@@ -518,7 +604,7 @@ static void reclaim_consumed_buffers(struct port *port)
                 return;
         }
         while ((buf = virtqueue_get_buf(port->out_vq, &len))) {
-                free_buf(buf);
+                free_buf(buf, false);
                 port->outvq_full = false;
         }
 }
@@ -765,7 +851,7 @@ static ssize_t port_fops_write(struct file *filp, const char __user *ubuf,
                 goto out;
 
 free_buf: